1. Field of the Invention
The present invention relates to a method of controlling the temperature of a heater of a fixing unit for use in an electrophotographic printer type facsimile machine.
2. Description of Related Art
Some facsimile machines are designed to print out a transmission report after the transmission is over, thereby outputting information reporting on the facsimile transmission to the user.
Such information includes date of facsimile transmission, time length for transmission, ID number or telephone number of the receiving end, the total number of transmitted pages, and transmission results (e.g., Safely transmitted/Transmission failed/Busy line/Error pages).
The transmission report is not necessarily printed out when the transmission is over. The printing out of the transmission is usually set "ON" or "OFF" by the user before each transmission. Some facsimile machines retain the "ON" state until the transmission report is reset by the user, once the printing of the transmission report is set "ON".
Some facsimile machines are equipped with an electrophotographic printer as a print engine where a toner image formed on the surface of a photoconductive drum is transferred onto a print medium by a transfer roller. The print medium is then advanced to the fixing unit where the toner image is fused. The fixing unit includes a pair of heat rollers. One of the pair of heat rollers has a heater therein. A thermistor is located in proximity to the heat roller having the heater built therein and detects the temperature of the heat roller. When the print medium passes between the pair of heat rollers, the toner image is fused with the heat and pressure applied by the heat rollers.
No printing operation is performed during periods such as a standby period and a transmission period. The heater is switched off during the standby period and transmission period, thereby saving electric power.
The related art will be described with respect to a facsimile machine incorporating an electrophotography type printer.
Prior to sending a facsimile, the user inputs a command as to whether or not a transmission report should be printed and subsequently depresses a START switch. Upon depressing the START switch, the facsimile machine activates a transmitting operation for transmitting the information to the receiving end.
After the transmission is over, a check is made to determine whether TRANSMISSION REPORT has been set ON. If it is determined that TRANSMISSION REPORT has not been set ON, then the facsimile machine does not print out the transmission report, and the facsimile machine enters the standby state where the machine waits till the next transmission operation is activated.
If it is determined that the printing of the transmission report has been set ON, the heater is energized to heat the heat roller to a fixing temperature Tf. The thermistor detects the temperature of the heat roller. When the outputs of the thermistor reaches a predetermined value or fixing temperature Tf, the transmission report is printed out. Then, the print medium is ejected, and the printing operation of the transmission is over.
With the aforementioned conventional facsimile machine, if the TRANSMISSION REPORT has been set ON, the heater is supplied with electric power after the transmission of information is over. As soon as the heat roller reaches the fixing temperature Tf, the printing operation starts to print out the transmission report.
For example, if the fixing temperature Tf is 155.degree. C., it takes about 17 seconds for the heat roller to reach 155.degree. C. when an ambient temperature Ta is 25.degree. C. In other words, the printing operation of the transmission report starts 17 seconds after the facsimile has been sent to the receiving end.
The time period from the activation of transmission till the transmission report has been printed out is the sum of the time for sending information to the receiving end, the time for heating up the heat rollers, and the time for printing the transmission report. The total time required is too long.